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Author Topic: Creating a biomechanical arm.  (Read 2932 times)
malcontentcontent
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« on: March 10, 2009, 07:25:18 am »

I've decided I need a "biomechanical" arm.  I've drawn up the plans, and I'm gathering materials now; however, I do have some questions regarding one item I intend to use.

For the shoulder joint, I'm contemplating using a portion of vinyl hose, the type one might employ as a vent for an electric clothes dryer.
I've provided this like for reference: http://www.hardwareandtools.com/invt/6753586

Now, I have never worked with (or even personally seen) such an item before, and there are several things I'm wondering about.

1.  In regard to weight and flexibility, if I get a hose of the proper diameter (7 inches or so), do you think a person wearing this would be able to move their arm effectively?

2.  Do you think spray paint will take to it?

3.  Will the hose be durable enough for such an application?

I'd appreciating hearing any thoughts you may have.
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von Corax
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« Reply #1 on: March 10, 2009, 08:04:46 am »

That looks like standard dryer-vent hose, and in my experience that stuff is just about as flexible as an arms-dealer's morals. I wouldn't want to rely on its durability, however, as it's not intended to be flexed repeatedly. Your best bet would be to go to any large hardware or home-improvement store and look at the stuff in person.

Also, I'm given to understand that vinyl can be difficult to paint, although there are specially-formulated vinyl dyes which are quite effective.
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malcontentcontent
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« Reply #2 on: March 10, 2009, 08:27:38 am »

Thanks!

I had heard about vinyl being troublesome to paint.  Blast it!  Spray paint is just so easy to work with.  I love the stuff, but I know it's not always the best choice. 

I'm sure you're also correct about having to go look at the vent hose in person.  In all honesty, I'd rather not use this vinyl hose at all, because as you've pointed out, it's not really designed for flexing repeatedly.  The local hardware store has something similar made of aluminum, but I would run into the same issue with repeated flexing and I believe most of them are insulated with fiberglass (eek).

I'm thinking about alternatives, but nothing has come to mind so far.  Hmm.  I guess it's back to the drawing board.
« Last Edit: March 11, 2009, 03:23:20 am by malcontentcontent » Logged
Capt. Morion
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« Reply #3 on: March 12, 2009, 06:30:32 am »

When I built my mechanical arm some years ago I constructed a shoulder pauldren out of craft foam which attached to the inside of the shirt that I wore. The 'mechanical' components were woven steel tubing bolted to drain clamps that secured above my bicep (under the pauldren), above and below the elbow and at the wrist. There were craft foam armour plates along the back of my arm and over my hand and the entire thing was worn over a painted, arm length glove). It had decent flexibility (as much as one can expect) and was pretty easy to make. To mold the craft foam you heat it (either over a flame or with a hair dryer) and then stretch it over a form  (I used a basketball) while it cools. Seal it with glue and then paint.

Hope that helped,
Capt. Morion
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silastic armor fiend
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« Reply #4 on: March 12, 2009, 06:35:08 am »

that sounds really cool. id like to see some pictures if its not too much trouble.
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malcontentcontent
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« Reply #5 on: March 12, 2009, 08:41:49 am »

When I built my mechanical arm some years ago I constructed a shoulder pauldren out of craft foam which attached to the inside of the shirt that I wore. The 'mechanical' components were woven steel tubing bolted to drain clamps that secured above my bicep (under the pauldren), above and below the elbow and at the wrist. There were craft foam armour plates along the back of my arm and over my hand and the entire thing was worn over a painted, arm length glove). It had decent flexibility (as much as one can expect) and was pretty easy to make. To mold the craft foam you heat it (either over a flame or with a hair dryer) and then stretch it over a form  (I used a basketball) while it cools. Seal it with glue and then paint.

Hope that helped,
Capt. Morion
It does help, thanks! 

Pauldren.  That's the word.  I'll look into craft foam for the pauldren, but I'm really aiming for that accordion-like effect, and I don't know if I can come up with a design like that using craft foam.  I've heard good things about craft foam, so I will be experimenting with it.  I was also considering some type of light steel rings sewn into fabric, but there are so many other possibilities. 

Wow.  I had planned to do the same exact thing with the woven steel tubing (like the flexy kind used for sinks, right?).  How funny that we had similar ideas!

I picked up an aluminum vent yesterday, and it seems rather sturdy.  I'm going to start on the prototype this weekend.  I'll get my hands on some craft foam and begin working on some designs with that as well.  I want this thing to be as durable and comfortable as it possibly can be.
« Last Edit: March 12, 2009, 08:47:38 am by malcontentcontent » Logged
SilasHarridenMD
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« Reply #6 on: March 12, 2009, 11:05:35 am »

I was thinking of making the same type of arm using corrugated rubber hose, like the stuff on this gasmask
Spoiler (click to show/hide)
you can get it in varying guages, although i dont know where in america, in Aus you can by it at a store called clark rubber.
its called something like flexi hose, or mud pipe hose. and it has a metal wire running through it,
Spoiler (click to show/hide)
looks great, rubber finish, not shiny at all. and its ment to bend.
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silastic armor fiend
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« Reply #7 on: March 12, 2009, 11:35:17 am »

id really like to know where to get that. i dont think we have any clarks rubber kind of stores over here. certainly not in my area
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stockton_joans
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« Reply #8 on: March 12, 2009, 01:09:28 pm »

you could always try making one from leather with metal rings inside to give the ridges
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« Reply #9 on: March 12, 2009, 01:40:49 pm »

If you're looking for a big bendy corrugated pipe perhaps look into vinyl ducting? I know you can get that on ebay Smiley
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malcontentcontent
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« Reply #10 on: March 12, 2009, 06:53:41 pm »

If you're looking for a big bendy corrugated pipe perhaps look into vinyl ducting? I know you can get that on ebay Smiley
I was definitely considering vinyl ducting, as we discussed above.  The conclusion we came to was that it was not meant for repeated flexing and therefore may not be durable enough for this project.  Ebay is a wonderful resource, however!

id really like to know where to get that. i dont think we have any clarks rubber kind of stores over here. certainly not in my area
I cannot think of anything.  Alas, I think our best option would be to place orders with online retailers.  Perhaps, after receiving payment via Paypal, one of our fellows in Australia would be willing to make the purchase on our behalf and send it over.

you could always try making one from leather with metal rings inside to give the ridges
I am not yet confident enough in my craftsmanship to attempt such a feat. Tongue
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« Reply #11 on: March 12, 2009, 07:15:09 pm »

If you're looking for a big bendy corrugated pipe perhaps look into vinyl ducting? I know you can get that on ebay Smiley
I was definitely considering vinyl ducting, as we discussed above.  The conclusion we came to was that it was not meant for repeated flexing and therefore may not be durable enough for this project.  Ebay is a wonderful resource, however!
Ah sorry didn't see that Undecided I would have thought it was flexible enough though
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silastic armor fiend
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« Reply #12 on: March 12, 2009, 09:17:56 pm »

If you're looking for a big bendy corrugated pipe perhaps look into vinyl ducting? I know you can get that on ebay Smiley
I wonder how one would go about doing this? I imagine it would be very hard (if its even possible) for somebody to do this without help. Any ideas?
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malcontentcontent
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« Reply #13 on: March 12, 2009, 09:45:20 pm »

Ah sorry didn't see that Undecided I would have thought it was flexible enough though
No worries, mate.  Smiley I intend to give the vinyl hose a go, anyway, only to see how it goes.  I'm just looking for other options as well.  I want to make several different pieces and then test them out.
« Last Edit: March 12, 2009, 09:47:18 pm by malcontentcontent » Logged
Capt. Morion
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« Reply #14 on: March 13, 2009, 01:55:20 am »

that sounds really cool. id like to see some pictures if its not too much trouble.
I'm actually not sure I have any photos of it (it was several years ago and the arm has since been sold) but I'll look when I get back to my other computer.
When I built my mechanical arm some years ago I constructed a shoulder pauldren out of craft foam which attached to the inside of the shirt that I wore. The 'mechanical' components were woven steel tubing bolted to drain clamps that secured above my bicep (under the pauldren), above and below the elbow and at the wrist. There were craft foam armour plates along the back of my arm and over my hand and the entire thing was worn over a painted, arm length glove). It had decent flexibility (as much as one can expect) and was pretty easy to make. To mold the craft foam you heat it (either over a flame or with a hair dryer) and then stretch it over a form  (I used a basketball) while it cools. Seal it with glue and then paint.

Hope that helped,
Capt. Morion
It does help, thanks! 

Pauldren.  That's the word.  I'll look into craft foam for the pauldren, but I'm really aiming for that accordion-like effect, and I don't know if I can come up with a design like that using craft foam.  I've heard good things about craft foam, so I will be experimenting with it.  I was also considering some type of light steel rings sewn into fabric, but there are so many other possibilities. 

Wow.  I had planned to do the same exact thing with the woven steel tubing (like the flexy kind used for sinks, right?).  How funny that we had similar ideas!

I picked up an aluminum vent yesterday, and it seems rather sturdy.  I'm going to start on the prototype this weekend.  I'll get my hands on some craft foam and begin working on some designs with that as well.  I want this thing to be as durable and comfortable as it possibly can be.
I'm a big fan of craft foam but it probably won't work for anything accordian-like. As far as durability goes, just pretty much drown the thing in glue (I paint it on but make sure to let it dry between coats) and it holds up pretty well.
I love the flexible steel tubing, it gives the piece a nice look since it's actually metal and it has a decent amount of flex to it.

I'd love to see pics of your arm when it's finished.
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« Reply #15 on: March 13, 2009, 02:18:56 am »


I'm a big fan of craft foam but it probably won't work for anything accordian-like. As far as durability goes, just pretty much drown the thing in glue (I paint it on but make sure to let it dry between coats) and it holds up pretty well.
I love the flexible steel tubing, it gives the piece a nice look since it's actually metal and it has a decent amount of flex to it.

I'd love to see pics of your arm when it's finished.

Dipping it in latex (or brushing on) would be a better bet for a flexible item. I think you'd find glue would crack pretty quickly and start flaking.
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« Reply #16 on: March 13, 2009, 05:50:36 am »


I'm a big fan of craft foam but it probably won't work for anything accordian-like. As far as durability goes, just pretty much drown the thing in glue (I paint it on but make sure to let it dry between coats) and it holds up pretty well.
I love the flexible steel tubing, it gives the piece a nice look since it's actually metal and it has a decent amount of flex to it.

I'd love to see pics of your arm when it's finished.

Dipping it in latex (or brushing on) would be a better bet for a flexible item. I think you'd find glue would crack pretty quickly and start flaking.
I've never used it for a flexible application before (just static armour pieces) so that's what my suggestion was based off of but the latex sounds like a good idea to retain some flexibility, I'll file that away for when I get around to recreating my arm
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